The lower limbs of the human body, namely the femur (thigh bone), the tibia (shinbone), and fibula, are designed to bear the weight of the body and to provide the body with sufficient stability. The femur courses medially from its proximal end connected to the hip bone to its distal end connected to the knee, placing the knee joints closer to the body's center of gravity and thus giving the body better balance while walking or standing. The tibia and fibula, which are connected together by an interosseous membrane, extend in parallel from the knee to ankle, with the tibia being larger and located medially in relation to the fibula. The tibia articulates proximally with the femur, forming the hinge joint of the knee, and distally with the talus bone of the foot at the ankle, and as such receives most of the body's weight and transmits it to the foot, while the fibula, which articulates proximally and distally with the lateral aspects of the tibia, is a non-weight bearing bone and generally provides stability for the ankle joint. The shaft of the tibia is generally triangular in cross section, and its distal end is blunt where it articulates with the talus. Situated medially to such distal tibia end is the medial malleolus, and a fibular notch is provided on the lateral surface of the tibia opposite the medial malleolus.
The foot skeleton is made up of the tarsus, metatarsus, and phalanges bones, with the tarsus bones forming the proximal or heel end of the foot, the metatarsus bones forming the bases of the toes, and the phalanges being the toe bones. The tarsal bones include the talus, calcaneus, lateral cuboid, medial navicular, and medial, intermediate, and lateral cuneiform bones. The talus articulates with the tibia and fibula superiorly and is located on the upper surface of the calcaneus bone, which forms the heel and with the part that touches the ground the tuber calcanei, and such bones support most of the weight of the body, although some weight is distributed to the heads of the metatarsals by the arching of the foot. In some patients the ankle joint or interconnection of the lower end of the tibia, the fibula, and the talus (spaced apart by articular cartilage and held together by various ligaments) can become worn or injured due to a degenerative condition or deformity, or a fracture, subluxation, or other traumatic event. In order to stabilize the ankle joint and control the often severe pain caused by such conditions, an arthrodesis procedure may be necessary to fuse and therefore permanently immobilize the ankle joint, fusing the distal end of the tibia with the talus. Where both the tibi-talar and talocalcaneal joints are damaged, such as in some patients having severe osteoporosis, the calcaneus bone will also be fused with the ankle. Such tibiotalacalcaneal arthrodesis procedures today are typically accomplished by permanent intramedullary nailing, wherein after the ankle bone surfaces have been prepared a rigid nail or rod is inserted in a hole drilled upwardly through the calcaneus and talus bones and into the medullary canal of the tibia. Screws are passed laterally through holes drilled in the tibia to hold the proximal end of the nail in place in the tibia, and into the nail through holes drilled in the calcaneus and talus bones. A limitation of known intramedullary or tibio-calcaneal arthrodesis nailing systems is in obtaining sufficient compression across the arthrodesis site so that a proper fusion is accomplished. The present inventor has devised an arthrodesis implant or intramedullary nail and system wherein proper compression across the arthrodesis site can be obtained, as well as an improved arthrodesis nail outrigger assembly.